Safety belt pretensioners are generally equipped with a pyrotechnical pretensioner drive. Such pretensioners have proven to be very suitable in practice; however, they are expensive and are therefore employed to a limited extent, only.
There is a need for simple safety belt system pretensioners being easy and inexpensive to manufacture, working reliably, and whose use might be widespread due to low manufacturing costs.
One may take into consideration to derive the drive force necessary for pretension from a stressed spring being suddenly unstressed by a vehicle-sensitive release mechanism. But as high drive forces are needed for efficient belt system pretension in order to carry out pretension within a few milliseconds, very strong springs would have to be used.
One has hitherto not succeeded in providing a release mechanism for a spring being dimensioned to be correspondingly strong which keeps releasing safely at a predetermined vehicle deceleration rate even after years of stand-by condition, which may be manufactured to be as simple and inexpensive as the pretensioner itself and at the same time provides for high safety against unwanted release due to bumps, shocks and the like.
It is the underlying object of the invention to provide a pretensioner for safety belt systems which has a simple design and may be manufactured inexpensively, but nevertheless meets high requirements with respect to reliable function and safety against unwanted release.